Drawing hollow articles



July 12,1932. E.- DE RIDDER ET AL DRAWING HOLLOW ARTICLES Filed Sept. 20, 1929 Fig.1.

ww Sd A T7QC h m n mfl 7 e 3. H

By WM,

Patented July 12, 1932 UNITED STATES PATENT OFFICE ERNST DE BIDDER AND HUBER! ALTWICKER, OF BITTERFELD, GERMANY, ASSIGNORS TO I. G. FABBENINDUSTRIE AKTIENGESEILSCHAFT, OF FRANKFORT-ON-THE-MAIN, GERMANY, A CORPORATION OF GERMANY DRAWING HOLLOW ARTICLES Application filed September 20, 1929. Serial No. 394,119.

, sheets by embossing or drawing requires a metal which is ductile to a high degree, and which, therefore, must posses a high elongation. Although the elongation of technically pure magnesium and of quite a number of magnesium alloys, in the form of sheets, when subjected to the usual tensile strength tests exceeds 15 percent, it has been found practically impossible to draw hollow articles from such sheets in the cold state, as they prematurely tear under the stress.

An investigation of the reasons for this remarkable phenomenon shows that in magnesium and magnesium alloy sheets the transverse properties are of such a nature. and are so related to the longitudinal properties that in drawing operations the ultimate transverse strength of the metal sheet is exceeded before it is possible to place suflicient work in the metal to produce a definite deformation of the sheet. Therefore, before the drawing operation can produce deformation by elongation in the magnesium or magnesium alloy sheet, the sheet fails because its transverse strength is exceeded.

It appears that, with other metals, the ratio betweenlongitudinal and transverse tensions is immaterial with respect to the drawing of sheets in this manner as in that case the longitudinal stresses brought to bear upon the metal generally effect the deformation devequals or exceeds 1. In the particular case sired before the utlimate transverse strength limit is attained.

We have now further found that, with a rise in temperature, the transverse and the longitudinal properties change in a decidedly different degree. It finally was discovered that there exists a range of temperature in the case of technically pure magnesium,- which, moreover, may be hardened by the addition of limited amounts of zinc and/or aluminum, and/or manganese-in which the transverse strength (K equals or exceeds the longitudinal strength limit (K When working in this temperature range, hollow articles may be produced from magnesium and these magnesium alloys, by drawing, without serious difliculty.

The following table represents, for various temperatures (column 1), corresponding values for the ratio K /K (column 2) and for the Erichsen indentation values in mm. (column 3), in the case of an alloy consisting of 6.5% Al, 1% Zn, and traces of manganese (about 0.3 percent), balance magnesium.

Erichsen values Temperature mm represented, the minimum temperature required thus amounts to about 270 C. and is, in practice, preferably maintained at 350 C.

As mentioned above, we have further subjected sheets of a number of other alloys of I magnesium, especially those containing limited amounts of aluminum and/or zinc and/or manganese, to drawing and have found that the range of temperatures, within which the drawing should be performed, is about the same as in the case of the alloy specifically mentioned above. Among the alloys tested the following particularly lend themselves to drawing in the form of sheets:

About 15-22% manganese, balance magnesium. U

About 3.0% Zn, balance magnesium. About 3.0% Zn, 2% Al, balance magneslum.

In the last two alloys, as well as in the alloy containing.6.5% Al and 1% Zn already mentioned, small percentages of manganese (from 0.2 to 1.5 percent) may be present, which tend to diminish their liability to corrode without noticeably influencing their plasticity.

So as to further facilitate the drawing operation by relieving the material to be drawn of at least part of the strain set up by the friction of the die, we preferably back off the edge of the outer or receiving die in the manner exemplified by the accompanying drawing.

In this drawing, of which Fig. 1 is an elevation and Fig. 2 a ground plan, 1 indicates the receiving or outer die, 2 the inner die backed off at 3, the edge of the die being indicated by 4.

To further diminish the friction the usual lubricants as grease, oil, graphite, etc., may be employed in addition.

We have further found that it is rather essential to heat the dies to a temperature which causes a thermal filow from the dies to the workpiece, so as to maintain the temperature of the latter during the operation. Preferably therefore, the tools are heated to about 50 to 100 C. above the actual drawing temperature and maintained at this temperature during the drawing operation.

We claim:

1. The method of drawing hollow articles from sheets of magnesium and magnesium alloys which comprises drawing the sheets within a temperature range in which the transverse strength exceeds the longitudinal strength limit of the sheet.

2. The method of drawing hollow articles from sheets of magnesium and magnesium alloys which comprises drawing the sheets at a temperature amounting to at least 270 C.

3. The method of drawing hollow articles from sheets of magnesium and magnesium alloys which comprises drawin the sheets at a temperature of about 350 4. The method of drawing hollow articles from sheets of magnesium and magnesium alloys which comprises drawing the sheets at a temperature amounting to at least 270 C. 

